Thermal starting switch



Feb. 19, 1952 V FOULKE 2,586,321

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lnve t'or' Ted E. Foutke,

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Patented Feb. 19, 1952 THERMAL STARTING SWITCH Ted E. Foulke, ChagrinFalls, Ohio, assignor to General Electric Company, a. corporation of NewYork Application May 7, 1948, Serial No'. 25,688

6 Claims.

This invention relates to starting switches for electric dischargedevices, and more particularly to a thermal type starting switchparticularly suitable for low voltage fluorescent lamps.

The glow discharge starting switches now in wide use with fluorescentlamps provide for heating the filamentary electrodes and for impressinga high voltage for a short duration across the electrodes at starting.However, in certain situations, such as in railroad'service where 60volt D. C. is in use, starters of the glow discharge type are notavailable to operate at these voltages, and some other type of starteris required, for example, the so-called thermal starter. With thermalstarters of the type commercially available, considerable difficulty is.often encountered due to slow and uncertain restart. This comes about byreason of the series heater which keeps the starting contacts open. Uponfinal cooling, after the circuit has been opened and then reclosed, thecontacts slowly come" together and then begin to separate at theleastcontact. This action results in two serious disadvantages, one ofwhich is insufficient preheating of the electrodes if a start. doesoccur, and the other of which is the many attempted starts if the lampis not an easy starting one. In any event, the improper preheating ofthe electrodes on quick restart causes early failure of the lamp.

An object of my invention is to provide a new and improved thermalswitch for operating electric discharge devices.

Another object of my invention is to provide a new and improved thermalswitch which will provide for the necessary time delay in theapplication of the starting voltage to insure an adequate initialheating of the electrodes of the electric discharge device.

A further object of my invention is to provide a new and improvedsnap-acting thermal switch for electric discharge devices which willprovide adequate preheating time for the initial and also for each andevery repeated attempt of the discharge device to start or restart.

A feature of my invention is the provision of a new and improvedsnap-acting thermal switch which employs magnetic means opposingseparation of the contacts, when closed, to delay ultimate separationthereof and also opposing closing ofsaid contacts, when open, to delayultimate closing thereof.

In addition to the improved snap-acting thermal switch mentioned above,the present application discloses a new and improved circuit combinationof an electric discharge device with a thermal switch which has decidedadvantages over the circuits previously employed in the art. Thiscombination is characterized by positive starting of the lamps even onlow direct current voltages, and by constant preheating time,notwithstanding diificult and unusual starting conditions as mightresult, for instance, from a momentary interruption of the power supply.This circuit combination may be used with other types of startingswitches besides that specifically claimed in this parent application.Accordingly, it is being claimed in my divisional application Serial No.147,050, filed March 1, 1950, and assigned to the same assignee as thepresent invention.

Further features and advantages of my invention will appear from thefollowing detailed description of species thereof.

For a better understanding of my invention, reference may be had to thefollowing description taken in connection with the accompanying drawingsand its scope will be pointed out in the appended claims. Fig. 1 is adiagrammatic view of an electric discharge device and a starting andoperating circuit therefor incorporating my invention; Fig. 2 is anelevation, partly in section, illustrating in more detail thesnap-acting thermal switch shown in the starting and operating circuitof Fig. 1; Figs. 3 and 4 are perspective views of the snap-actingthermal switch of Fig. 2; Figs. 5 and6 are perspective views of amodification of the snap-acting thermal switch illustrated in Figs. 2, 3and 4; and Figs. 7 and 8 are elevations of portions of furthermodifications of switches comprising my invention.

Referring to Fig. l, I have there illustrated one embodiment of myinvention as applied to an.

electric discharge device I. The electric discharge device I, such as afluorescent lamp, therein illustrated comprises anelongated tubular orcylindrical envelope 2 having sealed into the ends thereof filamentaryelectrodes 3 and 4, each herein illustrated as comprising a coil,preferably in the form of a coiled coil of tungsten wire activated withoxides of alkaline earth metals such as a mixture of barium andstrontium oxides. The envelope 2 contains a gaseous atmosphere such as arare gas like neon, argon or mixtures thereof at a pressure of a fewmillimeters and a small quantity of mercury which, during the operationof the lamp, has a low pressure of the order of 10 microns. The device Imay be a low pressure positive column lamp of a fluorescent typeprovided with a suitable phosphor or fluorescent coating. Thisfluorescent coating, upon excitation by the radiation produced by anelectric discharge between the electrodes, transforms a shorter waveradiation due to the discharge into longer wave radiation such asradiation within the visible range. For ease of startin a stripe orstrip 5 of conductivematerial which, for example, may be a metallicpaint or graphite mixed with potassium silicate, may be applied to thesurface of device I. The starting strip 5 may be connected to one orboth of the electrodes.

In accordance with my invention, device I is connected across a suitablepower supply circuit 6, 6 which, for example, may be a 118 volt, 60cycle source, for supplying current to device I through the usualballast I which serves as a starting inductance. A manual make-and-breakcontrol switch 8 may be used to connect device I to the power supply. Astarting or heating circuit 9, 9' embodies a snap-acting thermal switchID in series with filamentary electrodes 3 and 4, and with ballast l inseries therewith, across the current supply 6, 6. A capacitance II of0.006 microfarads rating is preferably connected directly across thethermal switch III.

The snap-acting thermal switch I comprises a bimetallic strip I2actuated by a heater element I3 which is in series with ballast 1 acrossthe supply circuit 6, 6'. The bimetallic strip I2 carries an armature I4which is in magnetic coupling with a permanent magnet I5, so that whenstrip I2 deflects and opens a pair of normally closed contactscomprising a stationary contact I6 and a movable contact II, thearmature simultaneously coacts with the permanent magnet.

Referring to Fig. 2, the switch I8 is mounted on an insulating disc I8and enclosed in a suitable can or incasement I9. An insulating supportmember 20 mounted on disc I8 supports a pair ofternmerature-compensating elements 2| and 22 which are formed frombimetallic strips and are designed in such a manner so as to conform tothe shape of the bimetallic strip I2. Thus, when elements 2| and 22 andbimetallic strip I2 are mounted on support member 20 in a definite spacerelationship, these elements will retain this space relationshipregardless of the ambient temperature. Heater element I3 is mounted on apair of lead-in wires 23 and 24 supported by disc I8 in heat-transferrelationship to bimetallic strip I2. Permanent magnet I5, which, forexample, may be an insulating cylindrical-shaped magnet supported on arod 25, which is embedded in magnet I along its longitudinal axis, issupported by extensions 26 and 21 secured to the free ends of elements2| and 22, respectively. This insulating magnet may comprise a sinteredmixture of magnetizable metallic oxides, for example, a mixture of 30parts of F8203, 44 parts of F6304, and 26 parts of C0203.

Armature I4, comprising a cylindrical magnetic sleeve, substantiallysurrounds permanent magnet I5 and is supported by the free end of thebimetallic strip I2. Stationary contact I6 is secured to element 2| bymeans of an extension arm 28. Movable contact I! is securedito armatureI4 and is mounted thereon to engage stationary contact I6 when thebimetallic strip is in its inactive, or cold, position. It is sometimesfound desirable to mount an additional arm 28' to element 2| adjacentarm 28. Arm 28 usually comprises a long, thin deformable metallic stripwith stationary contact I6 mounted on the free end thereof. The size andweight of contact I6 may, when switch I6 is subjected to a shock, causearm 28 to obtain a permanent set. Thus, arm 28' serves as a bufier torestrain arm 28 from deforming to a point beyond its elastic limit whenexposed to shock. A pair of terminal contacts 29 and 30 are connectedthrough lead-in wires 3| and 32 to contacts I6 and I1 whereby to connectsaid contacts I6, IT to the filamentary electrodes of an electricdischarge device. The heater I3 is connected through leads 23 and 24 toanother pair of terminal contacts 38' (only one of which is shown inFig. 2).

Fig. 3 indicates the relative positions of the armature I4 and magnet I5when contacts I6 and I! are in their normally closed position,

while Fig. 4 indicates the relative positions of armature I4 and magnetI5 when the contacts I8 and H are in their open position.

Figs. 5 and 6 illustrate a modification of the thermal switch shown inFigs. 2, 3 and 4 and embody, in general, the same constituent partsthereof except that insulating permanent magnet I5 is replaced with aconductive permanent magnet 33. The cylindrical magnetic sleeve I4 isreplaced with a U-shaped armature 34, and rod 25 is replaced with anon-magnetic metallic support member 35 in the form of two strips ofbrass or copper between which the magnet is supported. The metallicsupport member 35 in turn is secured to the free ends of elements 2| and22. In order that contacts I6 and II, when open, be not short-circuitedby support member 35 directly contacting armature 34 on the sidesupporting movable contact an insulating sheet of mica 36 is secured tothe inner surface of armature 34. This insulating feature is necessaryin the type of switch employing a conductive permanent magnet. Thestationary contact I6 may be secured to an extension arm 31 of themetallic support member 35, which in turn is secured to element 2|. Fig.6 illustrates the position of the metallic permanent magnet 33 when thecontacts I6 and I1 illustrated in Fig. 5 are in the open position.

When the entire installation is energized as indicated in Fig. 1 byclosing switch 8, current flows through the ballast I, heater coil I3,filamentary electrode 3, bimetallic strip I2, contacts I1 and I6,element 2|, and filamentary electrode 4. Permanent magnet I5 retainscontacts I6 and I1 in their normally closed position for a predeterminedperiod 01' time until the stress and strain within the bimetallic stripI2, due to the heat transferred by heater element I3, overcomes themagnetic attraction of permanent magnet I5 for armature I4. At thispoint thermal switch I0, and more particularly the bimetallic strip I2,disengages the normally closed contacts with a snap action andthe-permanent magnet I5 engages another portion of armature I4 to retaincontacts I6 and H in an open position.

During the period of time contacts I6 and I1 are closed, the filamentaryelectrodes 3 and 4 are sufficiently heated to support an electricaldischarge therebetween, and the induced voltage supplied by theinductance 1 initiates .an are discharge between the electrodes 3 and 4.After an arc discharge has occurred between filamentary electrodes 3 and4, contacts I6 and I1 remain disengaged due to the discharge currentflowing through the series heater coil I3 which continually heats thebimetallic strip I2 and does not permit it to cool to that predeterminedtemperature at which point the strain within the bimetallic stripovercomes the magnetic attraction of magnet I5 for armature I4. If,however, device I should not start after the initial arc discharge hasoccurred or if it should be restarted immediately after having beenturned off, the magnetic attraction of the magnet and armature of mythermal switch will retain the contacts l6 and I! in their open positionuntil the bimetallic strip has cooled to a predetermined temperature. Atthis temperature, contacts l6 and I! will snap closed and will remainclosed until the bimetallic strip has been reheated and the filamentaryelectrodes 3 and 4 have again reached a temperature sufficient tosupport an arc discharge.

In Fig. '7 I have illustrated a modification wherein the mounting of thearmature and magnet is the reverse of that shown in the modificationspreviously described. To this end, a magnet 38 is mounted on thebimetallic element I2 and an armature 39 is fixedly mounted in properrelation thereto. The armature 39 may be mounted on a support membercorresponding to the members 25 and 35 in Figs. 2 and 5, respectively.

Whereas, in the modifications previously described, I have, in effect,provided a single magnet and armatures located on opposite sides of, andin the path of movement of, said magnet, in Fig. 8 I provide amodification employing a single armature 40 mounted on the bimetallicelement 12, and in effect, two magnets mounted on opposite sides of saidarmature. In this case, the magnetic means is shown as ahorseshoe-shaped ma net 41 with the armature 40 located between poles ofthe magnet.

The operation of the modifications shown in Figs. 7 and 8 is essentiallythe same as that of the modifications shown in Figs. 2 and 5.

The above described new and improved snapacting switch performs thefunctions of a thermal switch, namely, to retain open a pair of normallyclosed contacts during the operation of a lamp, without the need forstoring in the switch a quantity of heat sufficient in itself to performthe holding open function mentioned above. The provision of a permanentmagnet replaces the need for the storage of a larger quantity of heatwhich in turn must be dissipated before closure of the switch contactsoccur. The snap-acting switch comprises a permanent magnet whichprovides a predetermined preheat period for filamentary electrodesassociated with the switch by retaining the switch contacts closed, and,then opening the contacts of the switch with a snap action to providethe greatest possible voltage impulse With the given starting circuitelements. Upon opening of the switch contacts, the magnet retains thecontacts open without the need of a large amount of thermal energy; allthat is required is a temperature gradient large enough to retain thebimetallic support for the movable contact in engagement with themagnetic means holding open the contacts. The result is a switch whichwill close a pair of contacts held open by a discharge circuit asrapidly, if not more rapidly than a thermal switch employing onlystorage of thermal energy to perform the same function.

It will be obvious to those skilled in the art that variousmodifications may be made in the switches comprising my inventionwithout departing from the spirit of the invention, including variationsin the construction and mounting of the magnet IE or 33 and armature I4or 34, and the appended claims are intended to cover any suchmodifications coming within the scope thereof.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A thermalswitch comprising a fixed contact and a movable contactcarried by a thermally-deformable actuating member, a substantiallycylindrical armature carried by said actuating member, and a permanentmagnet mounted within said armature to alternatively attract oppositesides of said armature when said actuating member is in either itsclosed-contact position or its open-contact position whereby to opposeboth opening and closing of said contacts, a conductive support membercarrying both said fixed contact and said magnet, said actuating memberand said support member providing circuit terminals for said contacts,said magnet being composed of insulating material in order to preventshort-circuiting said terminals when said contacts are open.

2. A thermal switch comprising a pair of thermally-deformable membersmounted in ambient temperature compensating relationship for maintaininga normally constant spatial interval therebetween, a heater elementmounted in heat transfer relationship with one of said members foractuation thereof, a pair of cooperating contacts carried by saidmembers, and means for delaying both the opening and the closing of saidcontacts, comprising a permanent magnet and a cooperating armaturecarried by respective ones of said members, said magnet and armaturehaving cooperating portions disposed to attract and hold each other ineither position of said one member corresponding to the open and closedcontact positions of said members.

3. A thermal switch comprising a pair of bimetallic strips of similarconfiguration and characteristics, and mounted in substantialparallelism for maintaining a normally constant spatial relationshiptherebetween despite variations in ambient temperature, a heater elementmounted in heat transfer relationship with one of said strips foractuation thereof, a pair of cooperating contacts carried by saidstrips, and means for delaying both the opening and closing of saidcontacts comprising a permanent magnet and a cooperating armaturecarried by respective ones of said strips, said magnet and armaturehaving cooperating portions disposed to attract and hold each other ineither position of said one strip corresponding to the open and closedcontact positions of said strips.

4. A thermal switch comprising a pair of thermally-deformable membersmounted in an ambient temperature compensating relationship formaintaining a normally constant spatial interval therebetween, a heaterelement mounted in heat transfer relationship with one of said membersfor actuation thereof, a pair of cooperating contacts carried by saidmembers, a substantially cylindrical armature carried by one of saidmembers and a permanent magnet carried by the other of said members andlocated to lie within said armature in order to alternately attractopposite sides of said armature when said one member is actuated toeither its closed or open contact position, whereby to oppose both theopening and the closing of said contacts.

5. A thermal switch comprising a pair of bimetallic strips of similarconfiguration and characteristics, and mounted in substantialparallelism for maintaining a normally constant spatial relationshiptherebetween despite variations in ambient temperature, a heater elementmounted in heat transfer relationship with one of said strips foractuation thereof, a pair of cooperating contacts carried by saidstrips, a substantially cylindrical armature carried by said one strip,

and a permanent magnet carried by the other oi. said strips and mountedwithin said armature to alternately attract opposite sides thereo! whensaid one actuating strip is in either its closed or its open contactposition, whereby to oppose both the opening and the closing 0! saidcontacts.

6. A thermal switch comprising a pair of bimetallic strips 01 similarconfiguration, dimensions and characteristics and mounted in substantialparallelism for maintaining a normally comtant spatial relationshiptherebetween despite variations in ambient temperature, a heater elementmounted in heat transfer relationship with one of said strips foractuation thereof, a

I pair of cooperating contacts carried by said strips,

a substantially cylindrical armature carried by said one strip, and apermanent magnet composed of substantially nonconductive materialcarried by the other of said strips and mounted within said armature toalternately attract opposite sides thereof when said one actuating striisin either its closed or its open contact position, whereby to opposeboth the opening and the closing 0! said contacts.

TED E. FOUIKE'.

REFERENCES crran The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,746,827 Fry et al Feb. 11, 19301,793,904 Carter et al Dec. 2. 1930 2,181,294 Blggs Nov. 28, 19392,238,282 I Ayers Mar. 25, 1941 2,302,250 Penn Nov. 17, 1942 2,305,583Hodgkins Dec. 15, 1942 2,388,951 Bower NOV. 13, 1945 2.412.883

Gasser Dec. 17. 1948

